Optical Sensor Pixel Doping Layout for Low Dark Current Gain
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Solution Overview
Problem
Current optical sensors face challenges in reducing dark current and enhancing gain while maintaining low leakage current, particularly in applications requiring high sensitivity and accuracy such as direct time-of-flight systems.
Innovation Solution
The optical sensing apparatus incorporates a substrate with specific doping regions, including an absorption region, field control region, carrier confining region, and contact regions, which are designed to generate and control photo-carriers efficiently. This configuration includes a carrier confining region with a first and second barrier region, a channel region, and a protection region to manage electric fields and carrier flow, allowing for operation as an avalanche photodiode or phototransistor with reduced dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical sensor uses conventional structures without specialized carrier confining regions, then the device complexity is lower, but the dark current is higher and gain is reduced
Solution Approach 1:
The carrier confining region is segmented into multiple doped regions (first doped region, second doped region, third doped region) with different doping concentrations and types, creating distinct functional zones that collectively achieve carrier confinement while managing device complexity through modular design
Solution Approach 2:
Different regions within the carrier confining structure have different doping concentrations and types (n-type vs p-type), creating localized properties that optimize carrier confinement in specific areas while maintaining overall device functionality and managing complexity through spatial differentiation
2Reliability
If the optical sensor increases gain through avalanche multiplication, then the sensitivity is improved, but the leakage current increases
Solution Approach 1:
The doping concentrations are precisely controlled with specific ratios (e.g., first peak doping concentration to second peak doping concentration ratio between 0.1 to 10) to optimize the electric field distribution for avalanche multiplication while suppressing leakage current through parameter optimization
Solution Approach 2:
The electric field distribution is dynamically optimized through the graded doping structure, creating strong fields in multiplication regions while maintaining lower fields in other regions, enabling conditional avalanche gain only where needed to improve sensitivity without excessive leakage
3Measurement precision
If the absorption region is fully embedded in the substrate with optimized positioning, then the measurement precision is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The absorption region is pre-positioned and fully embedded in the substrate before final device assembly, with its position predetermined relative to the carrier confining region (distance ratio between 0.5 to 1.2), allowing subsequent manufacturing steps to proceed with standard tolerances while achieving high measurement precision
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The described configuration effectively reduces dark current and increases gain by confining photo-carriers within a strong electric field region, enabling high sensitivity and accuracy in optical sensing applications, particularly in direct time-of-flight systems.
Implementation Method 1
The absorption region supported by the substrate and composed of a second material, the absorption region configured to receive an optical signal and generate photo-carriers in response to receiving the optical signal
Implementation Method 2
The carrier confining region formed in the substrate and between the absorption region and the field control region, where the carrier confining region includes a first barrier region and a channel region, where the first barrier region is doped with a dopant of the second conductivity type and has a first peak doping concentration
Data Source
AI summary
An optical sensing apparatus is provided. The optical sensing apparatus includes a substrate, one or more pixels supported by the substrate, where each of the one or more pixels includes an absorption region, a field control region, a first contact region, a second contact region and a carrier confining region. The field control region and the first contact region are doped with a dopant of a first conductivity type. The second contact region is doped with a dopant of a second conductivity type. The carrier confining region includes a first barrier region and a channel region, where the first barrier region is doped with a dopant of the second conductivity type and has a first peak doping concentration, and where the channel region is intrinsic or doped with a dopant of the second conductivity type and has a second peak doping concentration lower than the first peak doping concentration.